1. Field of the Invention
An embodiment of the present invention relates to an apparatus and control method for image reading, and an image forming apparatus. This apparatus can suitably be applied to an image reading apparatus that optically reads an original with a scanner, and also can suitably be applied to a digital copy machine or the like that forms an image based on image data that has been read.
2. Description of the Related Art
Traditionally, a three-line CCD sensor including three lines of red, green, and blue has been employed for reading a color image. In the three-line CCD sensor, red, green, and blue color filters are arranged on the light receiving surfaces of the three line sensors. It has a configuration in which the three line sensors are arrayed in parallel.
In the three-line CCD sensor, all the line sensors cannot simultaneously read the same part of the original. Therefore, a position shift between the lines in the original scanning direction is compensated for by a memory circuit that includes a line memory or the like. That is, time alignment of image signals read by the respective line sensors is carried out by using the memory circuit.
Also, a four-line CCD sensor has recently been produced as a commercial product. The four-line CCD sensor has a line sensor for monochrome reading to read a monochrome image in addition to the three-line CCD sensor. This line sensor for monochrome reading has no color filter arranged on its light receiving surface. References disclosing techniques related to CCD sensors are JP-A-2004-272840, JP-A-2004-180196, and JP-A-2003-274115 (Japanese Patent Application Publications (KOKAI)).
As for this four-line CCD sensor, it has been proposed that the light receiving area of the pixel is varied between the light sensor for monochrome reading and the three line sensors for color reading so that a monochrome original is read with high resolution while a color original is read with high sensitivity.
Meanwhile, in the traditional image reading apparatus, it is necessary to read an entire original, store its image data in a memory section such as a page memory, and determine a character area and a photograph area from the overall image. This is because proper features must be set in accordance with the character area and the photograph area when performing image processing.
In the case of reading an entire original and temporarily saving its image data into a page memory, a large-capacity page memory is required and it also takes time. For example, in the case where an A4-size sheet of an original is read with a resolution of 600 dpi, a capacity of about 35 Mbytes for monochrome, or a capacity of 105 Mbytes for color, which is three times more than the monochrome case, is necessary. Moreover, a work area is necessary in order to determine whether an image is of characters or a photograph on the basis of that area.
In this manner, a large-capacity memory is necessary to read a sheet of an original and store its image data. Therefore, images of plural originals must be stored as in N-to-1 to print images of plural originals on one sheet, for example, in 4-to-1 (N-to-1) in the case of printing four images on one sheet. A memory with a larger capacity is required.